Solved by a verified expert:BIOQ 1099 Lab

exercise: genetics of corn kernels

Name: /20

Part

A: monohybrid cross

Kernels of

corn on the same cob are all “siblings”, offspring of the same two

parents. The phenotypes of the parents are known: both parent plants had only dark-coloured

kernels (usually called “purple”). Their

offspring have a mix of both purple and yellow kernels. These corn kernels can therefore be used to

determine the genotypes of the offspring,

their parent plants, and how their genes are carried from one generation to the

next. Gregor Mendel used this kind of

genetic exercise to formulate his three laws of genetics.

Select 10 rows on your cob, and count

the total number of purple (or brownish) and yellow kernels.

Express the numbers from #1 as a

ratio. Then divide both numbers by

the smaller number to find a reduced ratio. (For example, if your ratio was 53 to 8,

divide both numbers by 8 to get 6.625 to 1.)

Which is the dominant trait, purple or yellow?

List the possible genotypes for each

phenotype (purple or yellow), using upper case letters for dominant and

lower case for recessive. Remember

that genotypes consist of pairs

of the same letters. (Example: if yellow is dominant, then use “Y” for

yellow alleles and “y” for purple alleles.)

Yellow

phenotype = genotype

Purple

phenotype = genotype

How could two parents with purple

kernels have offspring with a mix of purple and yellow kernels? What must the genotypes of the parent

plants have been?

Use one or more Punnett squares

to confirm your conclusion in #5.

With these parents, what would be

the expected ratios of each phenotype?

Do your results in #2 agree with

the expected ratios? Why might they

be different?

Part B: dihybrid cross

Count the numbers of each kind of

kernel in ten rows of the cob labeled “B”.

There are four phenotypes:

Purple

smooth

Purple

wrinkled

Yellow

smooth

Yellow

wrinkled

Express your results as a four-part ratio. (For example: 98 to 32 to 29 to 16) Then divide all four numbers by the

smallest of the numbers to get a reduced ratio.

Which two traits are

dominant? Which two traits are

recessive?

Using the appropriate upper and lower case letters, give the

possible genotypes for each phenotype.

Purple

smooth

Purple

wrinkled

Yellow

smooth

Yellow

wrinkled

What must the genotypes of the parent plants have been?

With these parents, what would be the expected ratios of

each phenotype?

Do your results in #9 to #10 agree with the expected ratios? Why might they be different?

Part C: human traits

Other factors

being equal, blue eyes occur in humans when an individual carries two recessive

genes for eye colour, and brown eyes occur when an individual carries one or

two dominant genes for eye colour. This

means that there are three possible genotypes, but only two possible phenotypes,

as follows (“B” represents a brown-eyed allele, and “b” represents a blue-eyed allele):

Genotype

Phenotype

BB

Brown eyes

Bb

Brown eyes

bb

Blue eyes

16. What possible gametes could be produced

by a blue-eyed individual? (Remember

that gametes are haploid.)

17. What possible gametes could be produced

by a brown-eyed individual?

18. Draw one or more Punnett squares to show a

cross between a brown-eyed mother and a blue-eyed father.

19. What is the probability that a child of the

parents in #18 will be brown-eyed?

Blue-eyed? (If there is more than

one possible situation in #18, treat each one separately.)

20. Draw one or more Punnett squares to show a

cross between two brown-eyed individuals.

21. What is the probability that a child of the

parents in #20 will be brown-eyed?

Blue-eyed? (If there is more than one possible situation in #20, treat

each one separately.)

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